1. Field of the Invention
This invention relates generally to recording apparatus and, more particularly, to a recording apparatus having a digital signal input for recording such input digital signal on a record medium.
2. Description of the Background
Digital tape recorders that use a rotary head to record an audio signal in the form of pulse code modulation (PCM) digital data on a magnetic tape are known. This kind of digital tape recorder is frequently called a rotary head-type digital audio tape recorder (R-DAT). In such R-DAT apparatus, a magnetic tape is obliquely wrapped around a small rotary drum of about 30 mm in diameter over an angular extent of 90.degree., for example. Two rotary heads having different azimuth angles are mounted on the rotary drum with an angular separation of about 180.degree. between them. These two rotary heads are rotated at a rate of 2000 r.p.m., for example, and the two rotary heads alternately scan the width of the magnetic tape by an amount corresponding to the tape wrapping angle of 90.degree.. Typically, the audio signal is sampled at a sampling frequency of 48kHz and each sampled value is processed in the so-called 16-bit linear quantization manner, thereby producing the PCM data. The PCM data is time-compressed by a time-compressing ratio based upon the tape wrap angle of 90.degree. at every 1/2 rotation period of the rotary head and is subsequently recorded on the magnetic tape by the rotary heads as a series of adjacent slanted tracks.
Upon playback, the PCM data is reproduced from the magnetic tape by the two rotary heads and is decoded, time-expanded, and then reconverted into an analog audio signal. In this kind of digital recorder, in addition to the PCM data, sub-codes such as a time code, a program number, a start identifying signal or the like are also recorded on each track in specified regions different than those where the PCM data is recorded. Generally, a switch is provided that permits the user to switch input sources, for example, between an analog audio signal and a digital signal, such as from a broadcast satellite or the like. The selected input signal is then apportioned between the two rotating heads and recorded in slant tracks on the tape. Upon playback, the signals reproduced by the rotary heads are amplified and passed through a switching circuit before being fed through an error correction circuit to a digital-to-analog convertor. The output from the error correction circuit is typically employed to detect the sub-code information, which is used to control a micro-computer included in the recording apparatus. In such digital recorders, if the digital audio signal at the input changes either by being interrupted or by having an altered sampling rate, the recorder continues in the recording mode and results in an unstable signal being recorded on the magnetic medium. Such unstable signal is undesirable and produces annoying clicks and the like during playback.